I Field of the Invention
The present invention relates to filters for trapping and collecting air-borne coating overspray which has been discharged from a coating spray gun or other application device and, more particularly, two filters utilized in spray coating booths having a movable wall of filter material.
II Description of the Prior Art
U.S. patent application Ser. No. 06/371412 filed Apr. 23, 1982, for process and apparatus for filtering spray coating particles from air, discloses a spray booth having a front movable wall composed of two layers of movable, flexible filter material supplied from a single continuous supplied roll and is incorporated by reference herein. The layers of filter material are composed of a mat of closely-spaced non-woven extruded polypropylene fibers forming a multiplicity of cells and randomly positioned non-woven polypropylene fibers extending from the mat into each said cell to provide sub-cells of sub-micron size openings. This filter cloth is non-conductive as were other filter cloths previously utilized in the industry, see U.S. Pat. No. 3,811,371, issued May 21, 1974, to Sheila Hardy.
Such non-conductive filter cloth allows electrically-charged paint to remain charged after it collects on the cloth. This charged paint is attracted towards grounded backup rollers or backup screens or grids in spray booths. The charged paint builds up opposite the rollers, grids or screens, and is sucked through the cloth electrostatically since the paint particles still carry a negative charge, this causes the rollers, grids, or screens to get wet and sticky with paint. When the paint dries, it causes the filter cloth to stick to the rollers, grids or screens and causes tearing of the cloth. When the filter tears, it is necessary to shut down the system to make repairs. This interferes with production and is quite costly.